(1) Field of the Invention
The present invention relates to porous lanthanum manganite sintered bodies and solid oxide fuel cells using such porous sintered bodies as materials for air electrodes.
(2) Related Art Statement
Since solid oxide fuel cells ("SOFC"s) operate at a high temperature of around 1,000.degree. C., an electrode reaction is extremely active, and the SOFCs need no noble metal catalyst such as platinum at all. Further, their polarization is low, and output voltage is relatively high. Thus, an energy-converting efficiency is far greater as compared with other fuel cells. In addition, since all the constituent materials are solid, the solid oxide fuel cell is stable and has a long life.
In order to develop SOFCs, it is important to look for materials stable at high temperatures. As a material for the air electrodes, sintered bodies of lanthanum manganite are considered promising (Energy General Engineering, 13, 2, pp 52-68, 1990). As such lanthanum manganite sintered bodies, lanthanum manganite sintered bodies having a substantially stoichiometrical composition and lanthanum manganite sintered bodies in which a part of A-sites (lanthanum-sites) are missing (manganese-rich composition) are known. It is reported that the weight of the lanthanum manganite sintered body in which a part of the A-sites are missing decreases when the temperature is raised from room temperature to 1,000.degree. C. (J. Electrochem. Soc. 138, 5, pp 1519 to 1523, 1991). In this case, the weight of the sintered body begins to decrease from near 800.degree. C.
In particular, porous sintered bodies composed of lanthanum manganite doped with Ca or Sr at A-sites are regarded promising as materials for air electrodes involving self-supporting type air electrode tubes.